Redox substoichiometry in isotope dilution analysis

Isotope dilution analysis using the redox substoichiometric principle has been applied to the determination of antimony content in metallic zinc. As the substoichiometric reaction, the oxidation of trivalent to pentavalent antimony with potassium permanganate was used, followed by separation of these species by the BPHA extraction of trivalent antimony. Determination of antimony contents less than 0.5 μg was found to be possible with good accuracy, without separation of zinc ions. The antimony content in metallic zinc was determined to be 19.7±0.8 ppm, in good agreement with the results obtained by the other analytical methods.     

Detection method for microchip separations

The features of analytical systems utilizing microfluidic devices, especially detection methods, are described. Electrochemical detection (EC), laser-induced fluorescence (LIF), mass spectrometry (MS), and chemical luminescence (CL) methods are covered. EC enables detection without labeling and has been used in recent years because of its low cost and sensitivity. LIF is the most generally used detection method in microchip separations. Use of LED as an excitation source for fluorescence measurement was also developed for the purpose of miniaturization of the entire system, including detection and separation. Although MS enables highly sensitive analysis, the interface between MS and micro channels is still under examination. This review with fifty-two references introduces interesting detection methods for microchip separations. Related separation methods using microfluidic devices are also discussed.     

Unperturbed chain dimensions of isotactic polypropylene in theta solvents

The unperturbed mean-square end-to-end distance 〈R₀²〉 and its temperature variation d In 〈R₀²〉/dT for isotactic polypropylene have been estimated from intrinsic viscosity data in three theta solvents, i.e., diphenyl, diphenyl ether, and dibenzyl ether, measured at their θ temperatures as determined by precipitation temperature measurements. The characteristic ratios, 〈R₀²〉/nl², where n is the number of bonds of length l in the main chain, evaluated by assuming Φ = 2.87 × 10²¹, are 5.80 in diphenyl (at θ = 125.1°C.), 5.41 in diphenyl ether (at θ = 142.8°C.), and 4.56 in dibenzyl ether (at θ = 183.2°C.). These values lead to the temperature coefficient d In 〈R₀²〉/dT = ?4.09 × 10^?3 deg.^?1 Results are compared with the data previously reported on polyethylene.     

Catalytic asymmetric synthesis of binaphthol derivatives by aerobic oxidative coupling of 3-hydroxy-2-naphthoates with chiral diamine-copper complex

Asymmetric aerobic oxidative coupling of 3-hydroxy-2-naphthoate with a copper complex prepared in situ from chiral diamine 3 and cuprous chloride as catalyst afforded binaphthol derivatives in good enantioselectivities up to 73% ee.     

Structure of a novel epidithiodioxopiperazine, emethallicin A, a potent inhibitor of histamine release from Emericella heterothallica

A new epidithiodioxopiperazine derivative, emethallicin A (1), was isolated along with ergosterol from the mycelial extract of the heterothallic fungus, Emericella heterothallica (mating type A). The structure of emethallicin A (1) was established on the basis of chemical and spectroscopic investigations and finally by chemical transformation to apoaranotin (11). Emethallicin A (1) has the same basic skeleton as apoaranotin (11), with C6-C2 carboxylic acid (mandelic and phenylacetic acids) diester moieties, and showed a potent inhibitory activity on histamine release from mast cells.     

N-nitrosamines via the phase-transfer mediated nitrosation of secondary amines with sodium nitrite and n-haloamides

Secondary amines are cleanly and readily converted to the corresponding N-nitrosamines in high yield under phase-transfer conditions by means of soduim nitrite and N-halo-amides; the active nitrosating agent is presumed to be dinitrogen tetroxide.